Communication apparatus and a method of controlling a communication apparatus

ABSTRACT

Communication apparatus having first communication device conformed to a first communication standard and second communication device conformed to a second communication standard different from the first communication standard. A control unit is coupled to the first and second communication device. The first communication device is capable of detecting whether or not another apparatus is disconnected from the first communication device. The control unit is capable of setting the second communication device in an active state if the first communication device detects that another apparatus is disconnected from the first communication device when the second communication device is in an inactive state. The second communication device is capable of being used to communicate with another apparatus when the second communication device is set in an active state, and is not capable of being used to communicate with another apparatus when the second communication device is set in an inactive state.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication apparatus adapted touse two or more different communication standards, in an electronicdevice capable of transmitting and receiving information data via adigital interface.

2. Related Background Art

Recently, apparatuses and systems for processing not only textinformation such as documents but also various information such asimages and sounds are beginning to be extensively used with theimprovement of the processing capability of a central processing unit(CPU) using a computer or the like, the progress of a graphicaloperating system (OS) for operating hardware, the increase in capacityand the progress of digitization of communication information in anetwork, and the development of information compression techniques.

With the development of such multimedia technologies, it is becomingpossible to transmit all types of data in all forms by all communicationprotocols via a single digital interface (digital I/F). It is alsobecoming possible for an apparatus corresponding to one communicationprotocol and incorporating a plurality of units to externally controleach unit and exchange information with external devices.

As an example of the digital I/F bus systems described above, acommunication system has been proposed in which AV devices, such as adigital video tape recorder (to be referred to as a VTR hereinafter), adigital television receiver, and a tuner, and a personal computer (to bereferred to as a PC hereinafter) are mutually connected by an IEEE1394serial bus (to be referred to as 1394 hereinafter), and digital videosignals and digital audio signals are transmitted and received betweenthese electronic devices. An outline of this 1394 system will bedescribed below.

As shown in FIG. 1, the 1394 system includes, as digital devices, a PCand a VTR corresponding to VGA (Video Graphics Array) inputs from adigital I/F, and a digital camera (to be referred to as a DCAMhereinafter) and a digital cam coder (to be referred to as DVCR)corresponding to VGA outputs from a digital I/F. The DVCR and the PC,the PC and the VTR, and the VTR and the DCAM are connected by the 1394serial bus described above.

Each digital device described above has a function of relaying digitaldata and control data on the 1394 serial bus. Also, a cable for the 1394serial bus includes three shielded twisted pair lines. Each twisted pairline is used to transfer protocol signals and data and supply electricpower. Therefore, the whole system can operate even when a certaindevice is turned off in the system.

The basic configuration of each digital device has an operation unit asa user interface, a display unit, a CPU for controlling the operation ofthe whole device, forming packets for communication, and holdingaddresses, a digital I/F for the 1394 serial bus, and a switch unit forperforming switching between a deck unit, a tuner unit, or a camera unit(neither is shown) and the digital I/F.

In this 1394 system, as shown in FIG. 2, communication is performed at apredetermined communication cycle (125 μs). Data having a time axis suchas video data or audio data is transmitted by isochronous (synchronous)communication by which a transfer band is guaranteed at a fixed datarate. Control data such as a control command is transmitted irregularly,where necessary, by asynchronous communication.

In communication like this, a cycle start packet exists at the beginningof each communication cycle, and a period for transmitting a packet forisochronous communication is set subsequently to the cycle start packet.A plurality of channels of isochronous communication can besimultaneously performed by assigning channel numbers to packets forisochronous communication.

For example, when channel 1 is assigned to communication from the DVCRto the VTR, the DVCR transmits an isochronous communication packet ofchannel number 1 onto the bus immediately after the cycle start packet.Meanwhile, the VTR monitors packets on the bus and receives the packetassigned with channel number 1. In this manner isochronous communicationis executed between the DVCR and the VTR.

Analogously, when channel number 2 is assigned to a packet from the DCAMto the PC, isochronous communication is executed between the DCAM andthe PC by transmitting the packet of channel number 2 onto the bus afterthe packet of channel number 1, and the isochronous communicationsbetween channel 1 and channel 2 are performed parallel. A period fromthe completion of transmission of all isochronous communication packetsin each communication cycle to the next cycle start packet is used inasynchronous communication.

Bus management by which the 1394 serial bus system described above canoperate will be described below.

An apparatus serving as a bus manager previously checks the networkstructure and the connection states of all nodes and controls buscommunication by defining each node ID and controlling isochronouscommunication.

That is, in the communication system as described above, when the powersupply is turned on or when a new digital device is connected or acertain device is disconnected, node IDs (physical addresses #0, #1, #2,and #3 in FIG. 3) are automatically assigned to the individual devices(nodes) in accordance with their connection states by the followingprocedure based on an address program and an address table stored in aninternal memory of the CPU, thereby automatically setting topology.

This node ID assignment procedure will be briefly described below. Thisprocedure includes determination of the hierarchical structure of thesystem and assignment of physical addresses to the nodes.

Assume that the above digital devices, i.e., the PC, DVCR, VTR, and DCAMare nodes A, B, C, and D, respectively.

First, each node transmits to a partner node, to which this node isconnected by the 1394 serial bus, information indicating that thepartner is its parent. While giving priority to a node firsttransmitting this information to its partner, the parent-childrelationship between the nodes in this system, i.e., the hierarchicalstructure of the system and a route node which is not a child of anyother node are finally determined.

More specifically, the node D informs the node C that the partner is aparent, and the node B informs the node A that the partner is a parent.If the node A informs the node C that the partner is a parent and thenode C informs the node A that the partner is a parent, a node whichfirst transmits the information to its partner is given priority. Thatis, if the transmission from the node C is earlier, the node A isregarded as a parent of the node C. As a consequence, the node A is nota child of any other node. If this is the case, the node A is a routenode.

After the parent-child relationship between the digital devices is thusdetermined, assignment of physical addresses is performed. This physicaladdress assignment is basically done in such a manner that parent nodespermit child nodes to perform address assignment and these child nodespermit themselves to perform address assignment from one connected tothe smaller port number.

When the parent-child relationship is determined as above in the exampleshown in FIG. 3, the node A first permits the node B to perform addressassignment. As a consequence, the node B assigns physical address #0 toitself. The node B sends this information onto the bus to inform theother nodes that “physical address #0 is already assigned”.

Next, the node A permits the node C to perform address assignment, andthe node C similarly permits the node D, i.e., the child of the node C,to perform address assignment. Consequently, the node D assigns physicaladdress #1, next to physical address #0, to itself, and sends thisinformation onto the bus.

Thereafter, the node C assigns physical address #2 to itself and sendsthis information onto the bus. Finally, the node A assigns physicaladdress #3 to itself and sends this information onto the bus.

A data transfer procedure will be described next.

Data transfer is enabled by assigning physical addresses as describedabove. In the 1394 serial bus system, however, arbitration of the bususe rights is performed by the route node prior to data transfer. Thatis, in the 1394 as shown in FIG. 4, only data of one channel istransferred at a certain timing. Therefore, the bus use rights must bearbitrated first.

When each node wants to perform data transfer, the node requests itsparent node to issue the bus use right. As a consequence, the route nodearbitrates the requests for the bus use rights from these nodes. A nodewhich acquires the bus use right as a result of the arbitrationdesignates the transmission rate before beginning data transfer. Thatis, the node informs the transmission destination node that thetransmission rate is 100, 200, or 400 Mbps.

Thereafter, in the case of isochronous communication, the transmissionsource node starts data transfer by the designated channel immediatelyafter receiving a cycle start packet transmitted by the route node as acycle master in synchronism with the communication cycle. Note that thecycle master transmits the cycle start packet onto the bus and alsomatches the time of the individual nodes.

In the case of asynchronous communication in which control data such asa command is transferred, on the other hand, after synchronous transferin each communication cycle is complete, arbitration for asynchronouscommunication is performed, and data transfer from the transmissionsource node and the transmission destination node is started.

In addition to the IEEE1394 standard described above, the RS-232Cstandard and the RS-422 standard presently exist and are used as theconventional serial data communication methods. These standards assumemutual connection using serial binary data exchange between a dataterminal equipment (DTE) and a data circuit-terminating equipment (DCE).These standards are formed and open to the public by the AmericanNational Standards Institute (ANSI).

As another example of the digital I/F bus systems, a universal serialbus (to be referred to as a USB hereinafter) as defined in UniversalSerial Bus Specification (Revision 1.0, Jan. 15, 1996) is proposed. Thisbus is invented as an external bus for connecting a PC and itsperipheral devices. An outline of this USB system will be describedbelow.

The connection form of the USB will be described with reference to FIG.3. This USB system comprises a host computer 300 such as a PC, a routehub 302, a first device 304 which is a recording medium such as a harddisk, a composite device 306 such as a camera-integrated VTR, a firsthub 308, a second device 310 such as a video camera, a third device 312such as a VTR, a second hub 314, a fourth device 316 which is an inputdevice such as a keyboard, and a fifth device 318 which is a pointingdevice such as a mouse. A hub has a function of adding a USB device.Also, a device is a terminal equipment including a USB bus interface(not shown). In this USB as shown in FIG. 3, the terminal equipments areconnected via the hubs including the route hub 302 on the host computer300, thereby forming a multiple star connection.

Since the host computer 300 has rights to access the first, second,third, and fourth devices 304, 310, 312, and 316, data exchange betweenthese devices is performed via the host computer 300. Therefore, busarbitration between the devices is not performed.

In the USB, data transfer is performed by a frame whose unit is 1±0.05ms. FIG. 4 shows the structure of the frame in the USB. Packets arepacked in this frame in accordance with the purpose and transferred.Four types of packets are defined in the USB. The first one is a tokenpacket, the second one is a start-of-frame packet (to be referred to asan SOF packet hereinafter), the third one is a data packet, and thefourth one is a handshake packet. The frame is started by the SOFpacket.

The host computer 300 performs data transfer with a plurality of devicesby sequentially sending data transfer requests previously scheduled inthe frame. If data is large-amount data, such as image data, whichcannot be contained in a single frame, the host computer 300 divides thedata in units of frames and transfers the divided data.

Packet fields are packed in the above four types of packets inaccordance with the purpose and transferred. In the USB, six types ofpacket fields are defined. The first one is an 8-bit packet identifierfield (to be referred to as a PID hereinafter), the second one is a7-bit address field (to be referred to as an ADDR hereinafter), thethird one is a 4-bit endpoint field (to be referred to as an ENDPhereinafter), the fourth one is an 11-bit frame number field, the fifthone is a 1- to 1023-byte data field, and the sixth one is a 5- or 16-bitcyclic redundancy checks field (the 5- and 16-bit ones will be referredto as a CRC5 and a CRC16, respectively, hereinafter). The four types ofpackets described above are constituted by combining these packetfields.

FIGS. 5A to 5D show the arrangements of the four types of packets. Asshown in FIG. 5A, the token packet is constituted by the combination ofthe PID, ADDR, ENDP, and CRC5 fields. As shown in FIG. 5B, the SOFpacket is constituted by the combination of the PID, frame number, andCRC5 fields. As shown in FIG. 5C, the data packet is constituted by thecombination of the PID, data, and CRC16 fields. As described above, thedata field has 1- to 1023-byte data. Also, as shown in FIG. 5D, thehandshake packet is constituted only by the PID.

In the USB, two transfer modes are defined. One is a full-speed transfermode whose average bit rate is 12 Mbps. The other is a low-speedtransfer mode whose average bit rate is 1.5 Mbps.

Also, four data transfer methods are defined in the USB. The first oneis isochronous transfer. In isochronous transfer, a transfer width whichis a data amount of transfer performed for each frame and a transfertime from transfer request to transfer start are guaranteed. Also, inisochronous transfer, no retransmission request can be made even if anerror occurs in transfer data. The second one is interrupt transfer. Ininterrupt transfer, only inputs from the individual devices to the hostcomputer 300 are possible. Also, in interrupt transfer, the datatransfer priority order on the bus is comparatively high. The third oneis bulk transfer. In bulk transfer, the data transfer priority order isthe lowest of the four transfer methods. The fourth one is controltransfer. Control transfer is performed to exchange setup data forsetting up the individual devices.

The 1394 serial bus system and the USB described above are communicationsystems which have not been put into practical use until recently, andthe conventional communication systems using RS-232C and RS-422 arestill extensively used presently.

The present situation, therefore, is that all of digital devicescorresponding to the 1394, digital devices corresponding to the USB, anddigital devices corresponding to RS-232C and RS-422 coexist.

Accordingly, it is expected that apparatuses including the interfaces ofboth the 1394 and the USB which are main streams in recent years will beextensively demanded. It is also expected that apparatuses includingboth the 1394 interface and the interface of RS-232C or RS-422 will beextensively demanded. Furthermore, it is expected that apparatusesincluding a plurality of interfaces of, e.g., the 1394, the USB, andRS-232C will be extensively demanded.

If, however, two or more types of communication devices are incorporatedinto a single apparatus to perform communication by two or morecommunication systems, the circuit scale is increased, and thissignificantly increases the cost.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovesituation, and has as its first object to provide a communicationapparatus, and a of controlling a communication apparatus, capable ofselecting two or more communication systems by using a single devicewithout increasing the cost due to an increase in the circuit scale ordeteriorating the operability in setting device connection.

According to a preferred embodiment of the present invention, there isprovided a communication apparatus having first communication meansconformed to a first communication standard, second communication meansconformed to a second communication standard different from the firstcommunication standard, and a control unit coupled to the first andsecond communication means. The first communication means is capable ofdetecting whether or not another apparatus is disconnected from thefirst communication means. The control unit is capable of setting thesecond communication means in an active state, if the firstcommunication means detects that another apparatus is disconnected fromthe first communication means when the second communication means is inan inactive state. Further, the second communication means is capable ofbeing used to communicate with another apparatus when the secondcommunication means is set in the active state, and is not capable ofbeing used to communicate with another apparatus when the secondcommunication means is set in the inactive state.

According to another preferred embodiment of the present invention,there is provided a method of controlling a communication apparatus thatincludes first communication means conformed to a first communicationstandard, and second communication means conformed to a secondcommunication standard different from the first communication standard.The method includes a step of detecting, using the first communicationmeans, whether or not another apparatus is disconnected from the firstcommunication means. The method also includes a step off setting thesecond communication means in an active state, if the firstcommunication means detects that another apparatus is disconnected fromthe first communication means when the second communication means is inan inactive state. In addition, the second communication means iscapable of being used to communicate with another apparatus when thesecond communication means is set in the active state, and is notcapable of being used to communicate with another apparatus when thesecond communication means is set in the inactive state.

Other objects, features and advantages of the invention will becomeapparent from the following detailed description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the connection form of an IEEE1394 serial bus;

FIG. 2 is a timing chart showing a communication example using theIEEE1394 serial bus;

FIG. 3 is a view showing the connection form of a USB;

FIG. 4 is a view showing a data transfer unit of the USB;

FIGS. 5A, 5B, 5C and 5D are views showing packets used in data transferof the USB;

FIG. 6 is a block diagram showing the arrangement of a digital videocamera of the first embodiment according to the present invention;

FIGS. 7A and 7B are views showing general formats of command data forthe IEEE1394;

FIG. 8 is a flow chart showing the flow of digital I/F switching controlaccording to the present invention;

FIG. 9 is a block diagram showing the arrangement of a video camera ofthe second embodiment according to the present invention;

FIGS. 10A and 10B are views showing data formats transmitted from a hostin bulk transfer;

FIG. 11 is a view showing ACK returned from an SD video camera of thisembodiment in bulk transfer;

FIG. 12 is a view showing the arrangement of a data packet in thisembodiment; and

FIG. 13 is a block diagram showing the arrangement of a digital videocamera using the data packet shown in FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first embodiment of the present invention will be described belowwith reference to the accompanying drawings. FIG. 6 is a block diagramshowing the embodiment in which the present invention is applied to avideo camera, i.e., a so-called SD (Standard Definition) video camera,for recording and reproducing an SD video signal.

Referring to FIG. 6, this SD video camera comprises a lens 1, an imagesensing device 3 such as a CCD, a camera processing unit 5, a recordingmedium 7 such as a magnetic tape, a helical scan head (to be referred toas a head hereinafter) 9, an error correction circuit (to be referred toas an ECC hereinafter) 11, a video signal processing circuit 13, aswitch circuit 15, an audio signal processing circuit 17, and a subcodedata processing circuit 19.

The SD video camera further comprises an auxiliary data processingcircuit (to be referred to as an AUX data processing circuithereinafter) 21, an arithmetic processing unit (to be referred to as anMPU hereinafter) 23, a format circuit 25, an interface circuit (to bereferred to as an I/F circuit hereinafter) 27, a read-only memory (to bereferred to as a ROM hereinafter) 29, a 1394 driver 31, an RS-232Cdriver 33, a 1394 I/O port 35, an RS-232C I/O port 37, a servo circuit39, a data bus 41, and a mode controller 43.

An object image taken through the lens 1 is photoelectrically convertedby the CCD 3 and subjected to predetermined signal processing by thecamera processing unit 5. Consequently, a luminance signal Y and colordifference signals V and U are generated at a ratio of 4:1:1 as digitalvideo signals. These digital video signals thus generated are input tothe switch circuit 15.

In performing encoding, the digital video signals are applied from theswitch circuit 15 to the video signal processing circuit 13 under theswitching control by the MPU 23. The video signal processing circuit 13performs compression coding for the 4:1:1 digital video signals by blockformation, discrete cosine transform (to be referred to as DCThereinafter), quantization, and fixed-length coding.

Also, in performing encoding, a digital audio signal is input from acircuit (not shown) such as a microphone or an audio amplifier to theaudio signal processing circuit 17 via the switch circuit 15 and encodedby the audio signal processing circuit 17. Additionally, subcode dataand AUX data are input from the MPU 23 to the subcode data processingcircuit 19 and the AUX data processing circuit 21, respectively, andprocessed by these circuits.

The video signal, audio signal, subcode data, and AUX data processed bythe video signal processing circuit 13, the audio signal processingcircuit 17, the subcode data processing circuit 19, and the AUX dataprocessing circuit 21, respectively, are input to the ECC 11 through thedata bus 41. The ECC 11 adds an error correcting code to these signals.The signals are then transmitted through a modulation circuit and a headamplifier (neither is shown) and written on the magnetic tape 7 with thehead 9.

In performing decoding, on the other hand, the head 9 reproduces digitalsignals from a track on the magnetic tape 7. The ECC 11 performs errorcorrection for the reproduced digital signals. Of the digital signalsoutput as digital block data from the ECC 11 to the data bus 41, thevideo signal processing circuit 13 connected to the data bus 41 decodesa video signal to generate a luminance signal Y and color differencesignals U and V at a ratio of 4:1:1. These generated signals are outputoutside via the switch circuit 15.

Of the digital signals output as digital block data from the ECC 11, anaudio signal is input, similar to the video signal, to the audio signalprocessing circuit 17 through the data bus 41. The audio signal isdecoded by the audio signal processing circuit 17 and output outside viathe switch circuit 15. Meanwhile, the subcode data processing circuit 19and the AUX data processing circuit 21 connected to the data bus 41input decoded subcode data and AUX data, respectively, to the MPU 23.

The compression-coded video and audio data are input to the formatcircuit 25 through the data bus 41. While the video signal processingcircuit 13 and the audio signal processing circuit 17 are performingencoding, the input video and audio data to the format circuit 25 aredata before the error correcting code is added by the ECC 11. On theother hand, while the video signal processing circuit 13 and the audiosignal processing circuit 17 are performing decoding, the input videoand audio data to the format circuit 25 are data after the errorcorrecting code is removed by the ECC 11.

The output subcode data and AUX data from the MPU 23 are also input tothe format circuit 25. The format circuit 25 reconstructs these videodata, audio data, subcode data, and AUX data into DIF data (digitalinterface data) and outputs these DIF data to the I/F circuit 27. TheseDIF data are packeted by the I/F circuit 27.

Note that the format circuit 25 and the I/F circuit 27 are so controlledby the MPU 23 as to perform processing suited to the selected one of the1394 interface and the RS-232C interface.

When the 1394 interface is to be used, the packet data formed by the I/Fcircuit 27 is supplied to the 1394 I/O port 35 via the 1394 driver 31.When the RS-232C interface is to be used, the packet data formed by theI/F circuit 27 is supplied to the RS-232C I/O port 37 via the RS-232Cdriver 33.

The 1394 driver 31 monitors the state of connection to the 1394 serialbus by detecting the power supply voltage of a power supply twisted pairline of 1394 twisted pair lines, and outputs data indicating theconnection state (to be referred to as 1394 connection state datahereinafter) to the MPU 23. The power supply voltage level of the powersupply twisted pair line is raised when the 1394 serial bus is connectedto the 1394 driver 31, and is lowered when the bus is disconnected.Therefore, the connection state can be detected by monitoring thisvoltage level.

The 1394 interface and the RS-232C interface can also be switched by theuser by operating an external select switch (not shown) or automaticallyswitched by, e.g., the MPU 23 by detecting the connections of theinterfaces.

Although the automatic switching between the interfaces will bedescribed later, the mode controller 43 switches the communication modes(switches the communication systems IEEE1394 and RS-232C) in accordancewith a setting signal (to be described later) sent from the MPU 23.

The servo circuit 39 controls the running of the magnetic tape 7 inaccordance with a designation signal from the MPU 23. Note that the MPU23 performs processing in accordance with input designating informationfrom an operation panel (not shown) and manages the operation mode ofthe whole system of this digital VTR and its various status transitions.

This servo circuit 39 primarily has a function of stationarilymaintaining the driving of a rotary drum and a capstan (neither isshown). That is, the servo circuit 39 is connected to a capstan motor(not shown) for controlling the tape feed speed, a capstan FG (FrequencyGenerator) for checking the rotating state of the capstan motor, a drummotor for rotating a rotary drum, and detectors FG and PG (PhaseGenerator) for checking the rotational speed and the rotational phase ofthe drum motor. These components are controlled by the servo circuit 39.

Command data for the SD video camera of this embodiment is externallyapplied to the 1394 I/O port 35. FIGS. 7A and 7B are views showinggeneral formats of the 1394 command data applied to the 1394 I/O port35. Referring to FIGS. 7A and 7B, CT and RC are 4-bit codes indicating acommand type and a response code, respectively. Table 1 below showscodes of the command type, and Table 2 below shows codes of the responsecode.

TABLE 1 CT/RC code (binary) MSB LSB Command type 0 0 0 0 Control command0 0 0 1 State inquiry command 0 0 1 0 Support inquiry command 0 0 1 1Report request command 0 1 0 0 (Unused) 0 1 0 1 (Unused) 0 1 1 0(Unused) 0 1 1 1 (Unused)

TABLE 2 CT/RC code (binary) MSB LSB Response code 1 0 0 0 Conditionsunfulfilled 1 0 0 1 Admitted 1 0 1 0 Rejected 1 0 1 1 Transiting 1 1 0 0Conditions fulfilled/standby 1 1 0 1 Already changed 1 1 1 0 (Unused) 11 1 1 Busy

Referring to FIGS. 7A and 7B, HA indicates a header address, and EHAindicates an extended header The header address is an 8-bit code andused as an identification code for a plurality of subdevices in onedevice connected to a communication interface (communication line). Thatis, the five upper bits of the header address indicate a subdevice typerepresenting the type of the subdevice, and the three lower bits of theheader address indicate a subdevice number representing the number ofthe subdevice among subdevices of the same type indicated by the fiveupper bits. The extended header address is a header address reserved forthe future. Table 3 below shows examples of the subdevice type.

TABLE 3 Code (binary) MSB LSB Subdevice type 0 0 0 0 0 Video monitor 0 00 0 1 (Unused) 0 0 0 1 0 (Unused) 0 0 0 1 1 (Unused) 0 0 1 0 0 Videocassette recorder (VCR) 0 0 1 0 1 TV tuner 0 0 1 1 0 (Unused) 0 0 1 1 1Video camera 0 1 0 0 0 (Unused) . . . 1 1 1 1 1

Referring to FIGS. 7A and 7B, OPC indicates an operation code, and OPRindicates an operand. The operation code indicates the contents ofcontrol with respect to a digital device connected to a communicationinterface (communication line). The operand indicates data required bythe operation code. Table 4 below shows examples of the operation codeand operand for reproduction.

TABLE 4 OPC OPR Reproduction 0xC3 Next frame 0x30 Lowest rate 0x31 Lowrate 4 0x32 Low rate 3 0x33 Low rate 2 0x34 Low rate 1 0x35 Normal rate(x1) 0x36 High rate 1 0x37 High rate 2 0x35 High rate 3 0x38 High rate 40x39 Highest rate 0x3A Preceding frame 0x3B

The unit of the data length of a command shown in FIGS. 7A and 7B isfour bytes. If the data length does not reach an integer multiple offour bytes, data in which all bits are zero is packed in the end of abit stream so that the data length is an integral multiple of four bytesas a whole.

When the user intends to cause the video cassette recorder (VCR) toperform normal reproduction in the case where the 1394 command datashown in FIGS. 7A and 7B are represented as shown in Tables 1 to 4, acode of command data such as “0x0021C336” (0x indicates hexadecimalnotation) is input from an external device. That is, the first “0x00”indicates four bits fixed to 0 at the beginning of the command data andsubsequent four bits (see Table 1) representing that the command data isa control command. The next “0x21” indicates an 8-bit header address andshows that the subdevice type is a VCR (see Table 3) and the subdeviceis the second device in the VCR. The next “0xC336” indicates anoperation code and an operand obtained from Table 4.

When this code for normal reproduction is input to the 1394 I/O port 35,on the basis of this input code the I/F circuit 27 generates an addressin the ROM 29 storing control data for normal reproduction and appliesthe address to the MPU 23. In accordance with the generated address, theMPU 23 reads out the control data from the ROM 29 and controls therotary drum and the capstan motor (neither is shown) via the servocircuit 39, thereby holding the reproduction state.

Meanwhile, command data for RS-232C is externally input to the RS-232CI/O port 37. In this embodiment, at least some command data of the 1394command data and the RS-232C command data are used in the both systems.

For example, command data received by the 1394 driver 31 and the RS-232Cdriver 33 by their respective communication systems and having the samefunction are used in the two systems. More specifically, assume that M(=integer of 2 or more) command data are transmitted and received byRS-232C and N (=integer of 2 or more, N≧M) command data includingcommand data having the same functions as the M command data aretransmitted and received by the 1394. If this is the case, all of the Mcommand data are used in both the 1394 and RS-232C. Alternatively, someof the M command data are used in the two systems.

With this arrangement, a communication device including the I/F circuit27, the MPU 23, and the like which perform various control operations byinterpreting command data can be shared by the 1394 communication systemand the RS-232C communication system. This eliminates the need toprovide a plurality of communication devices for various communicationsystems in one digital device. Accordingly, a digital devicecorresponding to both the 1394 and RS-232C communication systems can bemanufactured without increasing the circuit scale.

In RS-232C, two digital devices are usually connected in a one-to-onecorrespondence with each other. This makes device identification codes,device numbers, and the like data unnecessary. In this embodiment,therefore, a code such as “0xC336” is input to the RS-232C I/O port 37to indicate the same normal reproduction. Table 5 below shows examplesof the RS-232C reproduction codes corresponding to the 1394 controlcodes described above.

TABLE 5 Reproduction code Next frame 0xC330 Lowest rate 0xC331 Low rate4 0xC332 Low rate 3 0xC333 Low rate 2 0xC334 Low rate 1 0xC335 Normalrate (x1) 0xC336 High rate 1 0xC337 High rate 2 0xC335 High rate 30xC338 High rate 4 0xC339 Highest rate 0xC33A Preceding frame 0xC33B

When data is transferred by omitting the identification code and thedevice number of a device as described above, a delay time caused bycommand transfer can be reduced. This is convenient when RS-232C whichis a relatively-low-rate interface is used.

When this code for normal reproduction is input to the RS-232C I/O port37, on the basis of this input code the I/F circuit 27 generates anaddress in the ROM 29 storing control data for normal reproduction andinputs the address to the MPU 23. In accordance with the generatedaddress, the MPU 23 reads out the control data from the ROM 29 andcontrols the rotary drum and the capstan motor (neither is shown) viathe servo circuit 39, thereby holding the reproduction state.

In the above embodiment, the command data applied to the 1394 I/O port35 and the RS-232C I/O port 37 and having the same function are the samein the two communication systems. However, even when these command dataare different, an increase in the circuit scale can be prevented bygenerating common control data in the two communication systems from theROM 29 on the basis of the command data.

If this is the case, the I/F circuit 27 and the MPU 23 generate the samecontrol data for command data received by the 1394 I/O port 35 and theRS-232C I/O port 37 by their respective communication systems and havingthe same function. That is, the I/F circuit 27 which generates addressesin the ROM 29 storing control data corresponding to the command datareceived by the I/O ports 35 and 37 generates the same address in theROM 29 for the command data received by the two communication systemsand having the same function.

The above embodiment is described by using the IEEE1394 standard and theRS-232C standard. However, some other standard (e.g., the RS-422standard) can also be used. Also, when common command data is used fornot only a communication apparatus corresponding to two communicationstandards but also a communication apparatus corresponding to a largernumber of communication standards, the communication apparatus can bemanufactured without increasing the circuit scale.

In the above embodiment, the two lower bytes of the control command arethe same in the IEEE1394 standard and the RS-232C standard. However,this common part can have another arrangement. Additionally, the codelength for control is not limited to the above-mentioned code length(four bytes), so any arbitrary code length can be applied.

In this embodiment as described above, in an apparatus in which a givenone of a plurality of different communication systems is selected totransmit and receive command data for controlling devices connected to acommunication line, at least some of a plurality of command data of thedifferent communication systems or of a plurality of device control datagenerated on the basis of the received command data are used in all ofthese communication systems. Therefore, a common communication apparatusfor performing various control operations by interpreting the commanddata or the control data can be used in the different communicationsystems. That is, it is unnecessary to provide a plurality ofcommunication apparatuses for the different communication systems in onedevice. Consequently, it is possible to provide a communicationapparatus which can select two or more different communication systemsand does not largely increase the cost due to an increase in the circuitscale.

The automatic interface switching will be described below.

As described above, the 1394 driver 31 inputs the 1394 connection statedata to the MPU 23 in addition to the control data from the 1394 serialbus. If data indicating that the 1394 serial bus is connected is input,the MPU 23 supplies a 1394 setting signal to the mode controller 43 inorder to set the communication mode in the 1394 mode. Upon receiving the1394 setting signal, the mode controller 43 holds the 1394 driver 31active and holds the RS-232C driver 33 in sleep.

On the other hand, if the 1394 driver 31 is disconnected from the 1394serial bus, the power supply voltage of the power supply twisted pairline of the 1394 twisted pair lines drops. The 1394 driver 31 detectsthis voltage drop and outputs to the MPU 23 data indicating that the1394 driver 31 is disconnected from the 1394 serial bus. Upon receivingthis 1394 connection state data, the MPU 23 supplies an RS-232C settingsignal to the mode controller 43 in order to set the communication modein the RS-232C mode. When this RS-232C setting signal is input, the modecontroller 43 sets the 1394 driver 31 in sleep and the RS-232C driver 33active.

FIG. 8 is a flow chart showing the flow of interface switching control.Referring to FIG. 8, the control is started from step 0. In step 1, thecommunication mode is reset to the 1394 mode. In step 2, the 1394 driver31 is set active. In step 3, the RS-232C driver 33 is set in sleep.

In step 4, the level of the power supply voltage of the power supplytwisted pair line of the 1394 twisted pair lines is compared with athreshold voltage Th previously determined in the system to checkwhether the power supply voltage is higher than the threshold voltageTh. This threshold voltage Th is set to, e.g., 4 V.

If the power supply voltage of the power supply twisted pair line of the1394 twisted pair lines is higher than the threshold voltage Th, theflow returns to step 2. If this is the case, the processes in steps 2 to4 form a loop to hold the 1394 driver 31 active and the RS-232C driver33 in sleep.

On the other hand, if it is determined in step 4 that the power supplyvoltage of the power supply twisted pair line of the 1394 twisted pairlines is lower than the threshold voltage Th, the flow advances to step5. In step 5, the 1394 driver 31 is set in sleep. In step 6, the RS-232Cdriver 33 is set active. In step 7, the communication mode is set in theRS-232C mode. In final step 8, the control is completed.

Although not shown in the flow chart of FIG. 8, in this embodiment thepower supply voltage of the power supply twisted pair line of the 1394twisted pair lines is measured at fixed time intervals. If this measuredpower supply voltage is higher than the threshold voltage Th previouslyset in the system, the control start routine in step 0 is started.Therefore, even after the communication mode is set in the RS-232C mode,if the 1394 driver 31 is again connected to the 1394 serial bus, thecommunication mode is automatically switched to the 1394 mode.

In this embodiment as described above, it is unnecessary to provide aplurality of communication apparatuses for various communication systemsin one digital device. Therefore, a digital device corresponding to twocommunication systems of the 1394 and RS-232C can be manufacturedwithout increasing the circuit scale.

In this embodiment, data communication is performed in the 1394communication mode when the 1394 driver 31 is connected to the 1394serial bus. When the 1394 serial bus is disconnected, the RS-232C driver33 is automatically activated to perform data communication in theRS-232C communication mode. Therefore, even when a plurality of devicesare connected to both the 1394 serial bus and the RS-232C data channel,no connection setting operation need be performed, and high operabilitycan be realized.

Although the above embodiment is described by using the IEEE1394standard and the RS-232C standard, another standard (e.g., the RS-422standard) can also be used in place of the RS-232C standard.Alternatively, a communication line of any other standard than theIEEE1394 standard can be used, provided that the channel has a functionof supplying power.

The second embodiment according to the present invention will bedescribed below with reference to the accompanying drawings. FIG. 9 is ablock diagram showing the embodiment in which the present invention isapplied to a video camera, i.e., a so-called SD (Standard Definition)camera, for recording and reproducing an SD video signal. The secondembodiment differs from the first embodiment in that the firstembodiment includes the IEEE1394 and RS-232C as digital interfaces, butthe second embodiment includes the IEEE1394 and the USB. That is, thisembodiment discloses an apparatus in which at least some of command dataor of a plurality of device control data generated on the basis of thereceived command data are used in communication systems of both the 1394and the USB. The same reference numerals as in FIG. 6 denote the sameparts in FIG. 9, and a detailed description thereof will be omitted.

Referring to FIG. 9, this apparatus comprises a bit inversion circuit45, a USB driver 47, and a USB I/O port 49.

Video and audio DIF data are directly input from a data bus 41 to aformat circuit 25′. The format circuit 25′ also receives subcode dataand AUX data from an MPU 23, converts the data into DIF data, andoutputs the DIF data. This DIF data is packeted by an I/F circuit 27′.

The format circuit 25′ and the I/F circuit 27′ are so controlled as toperform processing suited to one of the 1394 interface and the USBinterface selected by the MPU 23.

When the 1394 interface is to be used, data is supplied to a 1394 I/Oport 35 via a 1394 driver 31. When the USB interface is to be used, datais supplied to the bit inversion circuit 45, the USB driver 47, and theUSB I/O port 49.

The 1394 and the USB transmit data by using different bit outputmethods; i.e., the most significant bit is transmitted first (MSB first)in the 1394, and the least significant bit is output first (LSB first)in the USB. When the USB is used, therefore, the bit inversion circuit45 performs bit inversion for data to be transmitted and received. Inthis embodiment, bit inversion is performed for data to be transmittedand received by the USB on the basis of the 1394. However, bit inversioncan also be performed for data to be transmitted and received by the1394 on the basis of the USB.

The 1394 interface and the USB interface can be switched by the user byusing an external select switch or can also be automatically switched bydetecting the connections of these interfaces.

The automatic interface switching will be described later.

As shown in the first embodiment, a code such as “0x0021C336” is inputfrom an external device when the user intends to cause a VCR to performnormal reproduction.

When this normal reproduction code is input from the 1394 I/O port 35,on the basis of the input code the I/F circuit 27′ generates an addressin a ROM 29 storing data for normal reproduction and applies the addressto the MPU 23. In accordance with this address data, the MPU 23 readsout the control data from the ROM 29 and controls a rotary drum and acapstan motor (neither is shown) via a servo circuit 39, thereby holdingthe reproduction state.

On the other hand, when the user intends to perform normal reproductionin the same manner as above by using the USB, a code is transmitted froma host (not shown) by the bulk transfer described earlier. In the bulktransfer, a token packet as shown in FIG. 10A is transmitted in thestart frame of the bulk transfer. In the next frame, the host transmitsa data packet as shown in FIG. 10B. A code such as 0x0021C336 describedabove is contained in a data field of this data packet. Transmission ofsuch comparatively small data is complete by two frames because data upto 1,023 bytes can be contained in the data field.

TABLE 6 PIDs of token packet PID name PID value OUT 11100001₂ IN01101001₂ SETUP 00101101₂

TABLE 7 PIDs of data packet PID name PID value DATA0 11000011₂ DATA101001011₂

The PIDs in the token packet will be described below. The first PID isOUT indicating that data transfer from the host is started, the secondPID is IN indicating that data transfer to the host is started, and thethird PID is SETUP indicating that device setup is started. Table 6above shows the values of these PIDs. Note that all token packets areissued by the host.

A data packet has two kinds of PIDs. If the data packet is not completein one frame, the first frame is started from DATA0, and PIDs aretoggled like DATA0/DATA1/DATA0/ . . . in units of frames. Table 7 aboveshows the values of these PIDs. In this embodiment, only one frame ofthe data packet is transmitted. Therefore, only DATA0 is used as the PIDvalue.

As described above, the USB and the 1394 have different bit outputmethods. In the USB, therefore, a code such as 0x0021C336 in the 1394described above arrives at the USB driver 47 in the form of a code suchas 0x0084C3CA formed by performing bit inversion in units of bytes.Accordingly, the bit inversion circuit: 45 converts a code having thevalue 0x0084C3CA into a code having the value 0x0021C336 by performingbit inversion in units of bytes, and outputs the converted code. In thisembodiment, the bit inversion circuit 45 is provided separately from theUSB driver 47. However, the USB driver 47 can also have this function.

When the transmission from the host is complete, the SD video camera ofthis embodiment informs the host of the completion of the transmissionby using a handshake packet as shown in FIG. 11. This handshake packetis constituted only by PID and changes the meaning of information inaccordance with the value of the PID. Table 8 below shows the values ofthe PID. ACK indicates that the communication is normally complete. NACKindicates that the data from the host has an error. If this is the case,the host repeats the same data transfer as above. STALL indicates thatthe SD video camera of this embodiment is made unable to perform datatransmission/reception for some reason.

TABLE 8 PIDs of handshake packet PID name PID value ACK 11010010₂ NACK01011010₂ STALL 00011110₂

When informed by ACK that the communication is normally completed, thehost again transmits the token packet to the SD video camera of thisembodiment in order to receive a response code. In the next frame, theSD video camera of this embodiment inserts, e.g., a response code0x0921C336, indicating that normal reproduction is possible, into a datapacket and transmits the data packet. When normally receiving the datapacket, the host transmits the ACK handshake packet to the SD videocamera of this embodiment to complete one transmission/reception.

In this embodiment, the control code and the response code are exchangedby using only bulk transfer. However, USB interrupt transfer can also beused in transmitting the response code. This configuration has theadvantage that the response code can be reliably returned even if thedata amount on the communication line is increased, since interrupttransfer has a higher transfer priority order than that of bulktransfer. Also, isochronous transfer can be used instead of bulktransfer in exchanging the control code and the response code.

USB communication can also be performed by adding additional informationto a data packet for performing the communication. FIG. 12 shows a wholedata packet when the additional information is added, and thearrangement of a data field in the data packet. This data packet istransmitted by, e.g., isochronous transfer. During the transmission, thedata field of the data packet is transmitted by a fixed length from thestart to the end of the communication.

In the data field shown in FIG. 12, a field to be transmitted first is adata_length field. The data length of the data_length field is set to,e.g., 1 byte. This field indicates an effective data length contained inthe data field in units of bytes. A fixed_length_data_field follows thedata_length field. This field is a fixed-length data field as describedabove. This field includes a valid_data field containing effective datato be actually decoded and a zero_pad_byte field in which data whosevalue is 0 is packed. If the data length of the valid_data field equalsthe data length of the fixed_length_data_field, the zero_pad_byte fielddoes not exist in the fixed length data field. The value of thezero_pad_byte field is not limited to zero, and some other data such as0xFF can also be used. The data length of the fixed_length_data_field isset to, e.g., 15 bytes.

In the data field shown in FIG. 12, an RS code field to be transmittedlast is an error detecting-correcting code such as a Reed-Solomon code.Although a Reed-Solomon code is used in this embodiment, another errordetecting-correcting code such as a Humming code can also be used. Inthis embodiment, a Reed-Solomon code having, e.g., 8 bytes is added.

FIG. 13 is a block diagram in which a communication apparatus using thedata packet shown in FIG. 12 is applied to an SD video camera. The samereference numerals as in FIG. 9 denote the same parts in FIG. 13, and adetailed description thereof will be omitted. Referring to FIG. 13, thisSD video camera comprises a second error correcting circuit (ECC) 51 anda second data bus 53.

When normal reproduction is to be performed, a code in which the valueof the valid_data field in the data field shown in FIG. 12 is 0x0021C336is applied from an external device to the USB driver 47 via the USB I/Oport 49. Since the effective data length is set to four bytes, the valueof the data_length field is 0x04. In fact, the value of the above datais bit-inverted in units of bytes. The bit inversion circuit 45 convertsthis bit-inverted value into a normal value. Each converted data issupplied to the second error correcting circuit 51 through the seconddata bus 53, and errors occurring on the communication line are detectedand corrected. In this embodiment, 4-byte correction is possible.

With the above arrangement, even in isochronous transfer in which aretransmission request cannot be made by NACK, the accuracy of data incommunication can be increased. Also, the use of isochronous transferhaving a comparatively high priority order has the advantage that theresponse can be rapidly performed in exchanging data. Note that the dataformat described above can contain not only the data length and theerror detecting correcting code but also some other additionalinformation. Note also that the numbers of bytes of the data_lengthfield, the fixed_length_data_field, and the RS_code field are notlimited to those of the above arrangement, so another arrangement cannaturally be used. Furthermore, although isochronous transfer is used inthis embodiment, the above arrangement is applicable to another transfersystem such as bulk transfer.

The automatic interface switching will be described next.

As described in the first embodiment, the 1394 driver 31 monitors theconnection of the 1394 by detecting the power supply voltage of a powersupply twisted pair line of 1394 twisted pair lines, and outputs theconnection state to the MPU 23. The USB driver 47 also monitors theconnection of the USB from the signal statuses of USB twisted pair linesand outputs the connection state to the MPU 23.

First, connection switching when the 1394 driver 31 is the master willbe described. In this case, 1394 connection is performed as much aspossible. The 1394 driver 31 applies a control signal from the 1394 busand the 1394 connection state data described earlier to the MPU 23.While the 1394 driver 31 is applying to the MPU 23 the data indicatingthat the 1394 bus is connected, the MPU 23 holds the 1394 driver 31active in order to set the communication mode in the 1394 mode. Also,upon receiving this 1394 setting signal, the MPU 23 holds the USB driver47 in sleep.

When the 1394 driver 31 is disconnected from the 1394 bus, the powersupply voltage of the power supply twisted pair line of the 1394 twistedpair lines drops, The 1394 driver 31 detects this voltage drop andoutputs to the MPU 23 data indicating that the 1394 driver 31 isdisconnected from the 1394 bus. When receiving this data, the MPU 23sets the 1394 driver 31 in sleep and the USB driver 47 active.

Next, connection switching when the USB driver 47 is the master will bedescribed. In this case, USB connection is performed as much aspossible. The USB driver 47 applies a control signal from the USB busand the USB connection state data described previously to the MPU 23.The USB bus signal operates as differential signals. The differentialsignals are D+ and D−. When the USB driver 47 is connected to the USBbus, one of the D+ and D− holds a voltage higher than a maximum valueV_(SE)(MAX) of a single-end threshold, and the other has a voltage lowerthan V_(SE)(MAX). The USB driver 47 detects this state and applies dataindicating USB bus connection to the MPU 23. While the USB driver 47 isinputting, to the MPU 23, the data indicating that the USB bus isconnected, the MPU 23 holds the USB driver 47 active in order to set thecommunication mode in the USB mode. Also, upon receiving this USBsetting signal, the MPU 23 holds the 1394 driver 31 in sleep.

When the USB driver 47 is disconnected from the USB bus, the voltages ofboth D+ and D− become lower than the voltage V_(SE)(MAX). If this statecontinues for 2.5 μsec or longer, the USB driver 47 determines that theconnection is cut. The USB driver 47 outputs, to the MPU 23, dataindicating that the USB driver 47 is disconnected from the USB bus. Uponreceiving this data, the MPU 23 sets the communication mode in the 1394mode. Also, the MPU 23 sets the USB driver 47 in sleep and the 1394driver 31 active.

The switching performed to set the 1394 or the USB as the master canalso be performed by the user by using a switch (not shown) or the like.Also, the 1394 can be set as the master by a standard operation, andthis can be reset when the power supply is turned on. Alternatively, theUSB can be set as the master by a standard operation, and this can bereset when the power supply is turned on. Any arbitrary setting can beperformed as long as the apparatus operates as above.

The above embodiments have been described by using two digital I/Fs.However, the present invention similarly applicable to an apparatusincluding three or more digital I/Fs such as the IEEE1394, the USB, andRS-232C.

In other words, the foregoing description of embodiments has been givenfor illustrative purposes only and not to be constructed as imposing anylimitation in every respect.

The scope of the invention is, therefore, to be determined solely by thefollowing claims and not limited by the text of the specifications andalterations made within the scope equivalent to the scope of the claimsfall within the true spirit and scope of the invention.

1. A communication apparatus comprising: a) first communication meansconformed to a first communication standard; b) second communicationmeans conformed to a second communication standard different from thefirst communication standard; and c) a control unit coupled to saidfirst and second communication means, wherein said first communicationmeans is capable of detecting whether or not another apparatus isdisconnected from said first communication means, wherein said controlunit is capable of setting said second communication means in an activestate, if said first communication means detects that another apparatusis disconnected from said first communication means when said secondcommunication means is in an inactive state, and wherein said secondcommunication means is capable of being used to communicate with anotherapparatus when said second communication means is set in the activestate, and is not capable of being used to communicate with anotherapparatus when said second communication means is set in the inactivestate.
 2. An apparatus according to claim 1, wherein the firstcommunication standard is an IEEE 1394 standard.
 3. An apparatusaccording to claim 1, further comprising a video signal processing unitcoupled to said first and second communication means, and adapted toprocess a video signal being provided to said first or secondcommunication means.
 4. An apparatus according to claim 1, wherein thesecond communication standard is one of a RS-232C standard, a RS-422standard, and a USB standard.
 5. An apparatus according to claim 2,wherein the second communication standard is one of a RS-232C standard,a RS-422 standard, and a USB standard.
 6. An apparatus according toclaim 5, further comprising a video signal processing unit coupled tothe said first and second communication means, and adapted to process avideo signal being provided to said first or second communication means.7. A method of controlling a communication apparatus that includes firstcommunication means conformed to a first communication standard, andsecond communication means conformed to a second communication standarddifferent from the first communication standard, said method comprisingthe steps of: detecting using the first communication means whether ornot another apparatus is disconnected from the first communicationmeans; and setting the second communication means in an active state, ifthe first communication means detects that another apparatus isdisconnected from the first communication means when the secondcommunication means is in an inactive state, wherein the secondcommunication means is capable of being used to communicate with anotherapparatus when the second communication means is set in the activestate, and is not capable of being used to communicate with anotherapparatus when the second communication means is set in the inactivestate.
 8. An apparatus according to claim 1, wherein said control unitis capable of setting said second communication means in the inactivestate, if said first communication means detects that another apparatusis connected to said first communication means when said secondcommunication means is in the active state.
 9. An apparatus according toclaim 8, wherein the first communication standard is an IEEE 1394standard, and wherein the second communication standard is one of aRS-232C standard, a RS-422 standard, and a USB standard.
 10. A methodaccording to claim 7, wherein the first communication standard is anIEEE 1394 standard.
 11. A method according to claim 7, wherein thecommunication apparatus includes a video signal processing unit coupledto the first and second communication means, and adapted to process avideo signal being provided to the first and second communication means.12. A method according to claim 7, wherein the second communicationstandard is one of a RS-232C standard, a RS-422 standard, and a USBstandard.
 13. A method according to claim 10, wherein the secondcommunication standard is one of a RS-232C standard, a RS-422 standard,and a USB standard.
 14. A method according to claim 7, furthercomprising the step of: setting the second communication means in theinactive state, if the first communication means detects that anotherapparatus is connected to the first communication means when the secondcommunication means is in the active state.
 15. A method according toclaim 14, wherein the first communication standard is an IEEE 1394standard, and wherein the second communication standard is one of aRS-232C standard, a RS-422 standard, and a USB standard.
 16. Anapparatus according to claim 9, further comprising a video signalprocessing unit coupled to the said first and second communicationmeans, and adapted to process a video signal being provided to saidfirst or second communication means.
 17. A method according to claim 13,wherein the communication apparatus includes a video signal processingunit coupled to the first and second communication means, and adapted toprocess a video signal being provided to the first or secondcommunication means.
 18. A method according to claim 15, wherein thecommunication apparatus includes a video signal processing unit coupledto the first and second communication means, and adapted to process avideo signal being provided to the first or second communication means.